Structure and optical properties of LiNbO3:ZnO (3.43–5.84 mol %) crystals

Abstract

LiNbO₃:ZnO (3.43–5.84 mol %) crystals have been studied using Raman spectroscopy and fullprofile analysis of X-ray diffraction data. The results demonstrate that, at ZnO concentrations above 3.95 mol %, their structure is free of Nb_Li basic defects, which are characteristic of congruent lithium niobate crystals. Increasing the Zn concentration leads to changes in the arrangement of structural units in the cation sublattice along the polar axis and distorts the BO₆ (B = Nb, Li, Zn, or a vacancy) oxygen octahedra. In the Raman spectra of the crystals, the width of the line at a frequency of 876 cm^–1, which corresponds to stretching modes of the oxygens in the BO₆ octahedra, has been shown to increase considerably, which may be due to changes in the character of bonding in the B–O–B bridges in response to changes in the Zn concentration in the crystals. The gradual increase in the electro-optical coefficients of the LiNbO₃:ZnO crystals with increasing zinc concentration can be accounted for by changes in the ionic contribution to these bonds.